In an electrolysis section of a hydrometallurgical zinc production system, a neutral solution leached and purified in a leaching section and purification section is mixed with a spent electrolyte to prepare an electrolyte of required composition, and this electrolyte is then subjected to electrolysis to cause deposition of metallic zinc on the cathodes so as to recover this electrolytic zinc. The zinc concentration in the electrolyte is gradually reduced with the progress of the electrolysis, and therefore, a purified fresh neutral leaching solution must be supplied to the electrolysis cells. According to common practice, after electrolysis, a predetermined amount of the electrolyte is sent to the leaching section, and a purified fresh leaching solution in an amount corresponding to the above amount of the electrolyte is mixed with the remaining part of the electrolyte to prepare a fresh electrolyte when the zinc concentration in the electrolyte is reduced to less than a predetermined setting. The fresh electrolyte is circulated through electrolysis cells. This method is called of preparation of electrolyte.
FIG. 1 shows schematically the process of preparation of electrolyte.
In the hydrometallurgical production of zinc, measurement of the zinc concentration in the circulating electrolyte is thus an important part of the electrolytic process. Automatic measurement of the zinc concentration in the electrolyte circulating through the cells can be attained by means as an on-stream fluorescence X-ray analyzer. However, employment of such a fluorescence X-ray analyzer involves various problems. For example, in the first place, this analyzer cannot be easily installed on the site of measurement due to the fact that it requires a bulky analyzing chamber. Secondly, great care must be given to the safety of operators due to the necessity for provision of a high-voltage power supply and in order to avoid the danger of exposure to the X-rays. Thirdly, the X-ray tube must be periodically replaced by new one resulting in troublesome maintenance and other operating problems. Fourthly, the equipment required for analysis is quite expensive such that it is not acceptable from the economical point of view. Due to various limitations as above described, the fluorescence X-ray analyzer is not commonly widely used.
As is commonly known, an instrument for measuring the sulfuric acid concentration is used in sulfuric acid plants for the purpose of automatic measurement of the sulfuric acid concentration. However, due to the fact that a platinum electrode is employed in this instrument, metals including zinc tend to deposit on the platinum electrode resulting in extreme fouling of the electrode. Thus, reliable measurement is difficult to attain when such instrument is used for measurement of the sulfuric acid concentration in the circulating electrolyte presently discussed.
An inductive solution analyzer is widely employed for the purpose of solution analysis since it has the advantage of ease of maintenance. However this inductive solution analyzer is not directly applicable to the desired automatic measurement of, for example, the zinc concentration in the circulating electrolyte due to the fact that the concentration value must be computed on the basis of an approximate expression. This concentration computation on the basis of such an approximate expression must be automatically carried out in order to attain the desired automatic measurement of the zinc concentration in the circulating electrolyte. Further, undesirable deposition of slurry on the transmitter of the inductive solution analyzer as well as objectionable intrusion of bubbles into this transmitter must be prevented in order that the zinc concentration in the circulating electrolyte can be continuously, automatically and reliably measured. For the above reasons, the desired continuous and automatic measurement of the zinc concentration in the circulating electolyte by the inductive solution analyzer has not yet been put into practical use.
One form of prior art inductive solution analyzers having a transmitter of bypass type is shown in FIG. 2. Referring to FIG. 2, the transformer portion of the transmitter of the inductive solution analyzer is disposed in a measuring cell 3 which has an inlet port 1 at the bottom thereof and an outlet port 2 at one side thereof. Thus, this measuring cell 3 is of the type in which a solution subject to measurement flows upward therethrough. However, utilization of such type of measuring cell for the measurement of the zinc concentration in the circulating electrolyte results frequently in such a trouble that slurry and bubbles tending to give rise to errors of measurement deposit on and attach to the transformer portion of the transmitter. This attributable to the structure of the measuring cell in the prior art inductive solution analyzer. More precisely, in this measuring cell, the solution subject to measurment, that is, in this case, the circulating electrolyte flows upward from the inlet port at the bottom toward the outlet port, tending to cause precipitation of slurry toward the bottom. Due to the fact that the inner diameter of the measuring cell is considerably greater than that of the inlet and outlet ports, the velocity of the circulating electrolyte is low in the measuring cell, and the slurry concentration in the circulating electrolyte is gradually increased in the vicinity of the transmitter thereby giving rise to deposition of the slurry on the wall of the liquid passage in the transformer portion of the transmitter. Further, many bubbles included in the circulating electrolyte tend to attach to the wall of the liquid passage in the transformer portion of the transmitter. Therefore the inductive solution analyzer of this kind has been unable to continuously and reliably measure the zinc concentration in the electrolyte circulating through the electrolysis cells. However, for the purpose of automation of the electolytic production of zinc, automation of the measurement of the zinc concentration in the electrolyte circulating through the electolysis cells in indispensable, and realization of this automatic measurement has been strongly demanded.